The present invention relates to a method for controlling output of alarm information in a system for monitoring a plant, such as a thermo-electric power generating plant.
A conventional monitoring system includes an input device, a computer, and a display device, and process variables at various locations or sensing points in the plant are scanned or sampled by means of the input device and read or stored in the computer. Each of the sampled analog type process variables is compared with a limit value dividing the normal and abnormal ranges, and when the process variable is found to be within the abnormal range, alarm information is outputted to attract the attention of a human operator and request him to take some appropriate measure. The alarm information may be in the form of an alarm message displayed on a CRT (cathode ray tube) display device. For instance, alarm messages in connection with 18 (eighteen) process variables can be displayed simultaneously on a single CRT device. When there are more process variables with which an alarm is to be produced, the alarm messages can be displayed on the same CRT in turn, and/or can be displayed on separate CRT's. When the plant is in steady state or the plant is running in a normal, expected manner, the number of alarm messages is limited and the operator can take measures responsive to the alarm messages without considerable delay. However, when unexpected troubles occur there can be so many alarm messages that it is difficult for the operator to cope with the situation. Particularly, it is difficult for him to find out which alarm needs immediate care and which one can wait, and there may occur a considerable delay in taking a necessary measure in response to a "serious" alarm. In addition, there may be considerable delay before some of the alarm messages are actually on the CRT screen, and alarms which require immediate attention may be included in those messages for which display was delayed. This can be another source of delay in responding to the "serious" alarm. Delay in taking a necessary measure can of course lead to a fatal breakdown of the plant.